For use with a brake cylinder having a body provided with a bore in which is slidably mounted a piston and a service brake-applying spring interposed between said body and one side of said piston for effecting a service brake application upon the release of fluid under pressure from the other side of said piston, a brake control valve device comprising;
- a. a first mechanically-operated fluid-pressure-released valve means having one position in which fluid under pressure can flow from a source of fluid under pressure to the other side of said piston to establish thereon a fluid pressure force to effect a brake release, and shiftable to a second position in which fluid under pressure is released from said other side of said piston to atmosphere to reduce said fluid pressure force thereby enabling said brake-applying spring to transmit, via said piston, a service brake-applying force variable in degree in accordance with the reduction in the degree of said fluid pressure force,
- b. a second mechanically-operated fluid-pressure-released valve means having one position in which fluid under pressure is released from said one side of said piston, and shiftable to a second position in which fluid under pressure can flow from a source of fluid under pressure to said one side of said piston to establish thereon a fluid pressure force which, in response to the flow of fluid under pressure from said other side of said piston to atmosphere in response to the shifting of said first valve means to its said second position, acts cojointly with said spring on said one side of said piston to transmit, via said piston, an emergency brake-applying force that exceeds in degree the maximum service brake-applying force obtainable solely from said spring,
- c. a spring-operated mechanical linkage, for effecting mechanical operation of said first and second mechanically-operated fluid-pressure released valve means,
- d. interlocking means so cooperating with said mechanical linkage and said first and second valve means as to preclude operation of said second valve means prior to operation of said first valve means to release all fluid under pressure from said other side of said piston,
- e. fluid-pressure-operated means for rendering said spring-operated mechanical linkage operable or inoperable to establish a force for effecting mechanical operation of said first and second mechanically-operated fluid-pressure-released valve means,
- f. a pair of differential-type fluid motors each operable upon the supply of fluid under pressure thereto to shift a corresponding one of said valve means to its said one position,
- g. operator-controlled means for so varying the pressure of fluid established in said fluid-pressure-operated means as to render said spring-operated mechanical linkage operable to establish an operating force for operating said first and said second valve means from their said first to their said second positions that is inversely proportional to the pressure of the fluid in said fluid-pressure-operated means, and
- h. a pair of electro-mechanical means each operable to control the supply and release of fluid under pressure to and from a corresponding one of said pair of differential-type fluid motors whereby each of said differential-type fluid motors is effective, so long as fluid under pressure is supplied thereto by its corresponding electro-mechanical means, to prevent operation of the corresponding one of said valve means from its said one to its said second position by said spring-operated mechanical linkage notwithstanding operation of said operator-controlled means as to so vary the pressure of fluid in said fluid-pressure-operated means as to render said spring-operated mechanical linkage operable to establish an operating force for operating said valve means from their said one to their said second position.